A touch screen display is a device that can detect an object in contact therewith or in proximity thereto. The touch screen display includes display layer covered with a touch-sensitive matrix that can detect a user's touch by way of a finger or stylus, for example. Touch screen displays are used in various applications such as mobile phones, tablets, and smartwatches. A touch screen display may enable various types of user input, such as touch selection of items or alphanumeric input via a displayed virtual keypad. Touch screen displays can measure various parameters of the user's touch, such as the location, duration, etc.
One type of touch screen display is a capacitive touch screen. A capacitive touch screen may include a matrix of conductive rows and columns overlaid on the display layer forming mutual capacitance sensors. In mutual capacitance sensors, a mutual capacitance at the intersection of each row and column of the matrix may be sensed. A change in mutual capacitance between a row and a column may indicate that an object, such as a finger, is touching the screen or is in proximity to the screen near the region of intersection of the row and column.
Touch screen displays employing mutual capacitance sensors employ a “forcing” signal that is applied to a column conductor of the capacitive touch matrix. A sensing of the coupled signal on respective row conductors is made to detect change in the mutual capacitance. Since the capacitance change caused by a finger is small, noise reduction is important in achieving satisfactory operation. One known source of noise is external noise injected from the environment. In order to achieve a high signal-to-noise ratio (SNR), this source of noise must be taken into account. The power of such external noise sources is often concentrated in a few harmonics.
While techniques exist for compensating for the introduced noise, the compensation provided may not be sufficient. A need accordingly exists in the art for the development of techniques for compensating for the introduced noise.